[aseipp]

U-Boot is implementing ACPI, yes, there was something at FOSDEM this year about it for ARM64 machines. QEMU can apparently now boot an arm64 virt machine with only ACPI tables and no device tree. This is all very recent. When I was working on a vague equivalent of systemd-stub last year as a fun exercise in UEFI development, I settled on U-Boot for UEFI and QEMU (but with virtualized device tree). I can't remember the specifics of what's unsupported by RuntimeServices when I was working on it. I'm like 99% certain it's not enough for SBSA compliance, at least.

Honestly, my opinion after all this was that UEFI is pretty convenient and nice, and I'm glad U-Boot has its own implementation, even if it isn't fully grown yet; UEFI for the executable spec with a DTB for bringing up the SOC with nothing else was nicer than a lot of embedded boot flows I've handled.